The objectives of this research project are to assess component processes and knowledge in reading and related language skills, in twins and siblings selected for deficits in reading and/or ADHD, and in normal- range control twins. Our previous focus on word recognition, orthographic and phonological coding, and phonological awareness will be supplemented with new measures of reading comprehension and higher-level language skills. Behavior-genetic analyses and assessment of the twins' literacy environments will be used to evaluate the genetic and environmental etiology for deficits in different component reading and language skills. Bivariate DF analyses and confirmatory factor analyses of twin data will be used to assess the genetic and environmental co- variance and/or independence among the component processes and knowledge. Behavior-genetic analyses will be used to validate subtypes and/or dimensions of individual differences among reading disabled children by assessing their differential genetic and environmental etiology. In collaboration with research projects I and IV, QTL analyses will be used to assess genetic linkage for deficits in different leading and language skills. Ne measures included in project II will allow the first thorough analysis of genetic and environmental influences on component processes in reading and listening comprehension.